The fabella sign is displacement of the fabella that is seen in cases of synovial effusion and popliteal fossa masses.
[1] The fabella is an accessory ossicle located inside the gastrocnemius lateral head tendon on the posterior side of the knee, in about 25% of people.
It can thus serve as a surrogate radio-opaque marker of the posterior border of the knee's synovium.
On a lateral radiograph of the knee, an increase in the distance from the fabella to the femur or to the tibia can be suggestive of fluid or of a mass within the synovial fossa.
[2] This medical sign article is a stub.